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Submarine canyons and channels are globally important pathways for sediment, organic carbon, nutrients and pollutants to the deep sea, and they form the largest sediment accumulations on Earth. However, studying these remote submarine systems comprehensively remains a challenge. In this study, we used the only complete-coverage and repeated bathymetric surveys yet for a very large submarine system, which is the Congo Fan off West Africa. Our aim is to understand channel-modifying features such as subaqueous landslides, meander-bend evolution, knickpoints and avulsions by analyzing their morphometric characteristics. We used a new approach to identify these channel-modifying features via morphometric fingerprints, which allows a systematic and efficient search in low-resolution bathymetry data. These observations have led us to identify three morphodynamic reaches within the Congo Canyon-Channel. The upper reach of the system is characterized by landslides that can locally block the channel, storing material for extended periods and re-excavating material through a new incised channel. The middle reach of the system is dominated by the sweep and swing of meander bends, although their importance depends on the channel's age, and the time since the last up-channel avulsion. In the distal and youngest part of the system, an upstream migrating knickpoint is present, which causes multi-stage sediment transport and overspill through an underdeveloped channel with shallow depths. These findings complement previous less- detailed morphometric analyses of the Congo Canyon-Channel, offering a clearer understanding of how submarine canyon-channels can store sediment (due to channel-damming landslides, meander point bars, levee building due to overspill), re-excavate that sediment (via thalweg incision, meander propagation, knickpoint migration) and finally transport it to the deep sea. This improved understanding of the morphodynamics of the Congo Canyon- Channel may help to understand the evolution of other submarine canyon- channels, and assessment of hazards faced by seabed infrastructure such as telecommunication cables. [ABSTRACT FROM AUTHOR]

The lower limits of petrophysical properties for an effective reservoir are among the key parameters for assessing hydrocarbon reserves and are therefore directly related to hydrocarbon exploration and development strategies. However, the lower limits for marine sandstone gas reservoirs are still not clear and the impact factors also remain to be discussed. This study analysed the lower petrophysical property limits of an effective sandstone reservoir in the Qiongdongnan Basin using porosity, permeability and gas testing. The results showed that the lower porosity and permeability limits of effective reservoirs developed in the deltas are 8.9% and 1.2 × 10−3 μm2, respectively, and 11.3% and 4.0 × 10−3 μm2 in the submarine canyons and fans, respectively. Sedimentary facies, sediment transport distance, grain size and burial depth of sandstone significantly influence the lower physical property limits. The lower porosity and permeability limits increase with the increase in sediment transport distance as well as the decrease in sandstone grain size and burial depth. Sediment sources and sedimentary facies determine whether sandstone can become an effective reservoir in the Qiongdongnan Basin. Specifically, the sediment source dramatically influences the petrophysical properties of sandstone. The sandstone sourced from the Red River has higher porosity and permeability, followed by the sandstone sourced from the Hainan Uplift, and the sandstone sourced from the palaeo-uplift within the basin has the lowest porosity and permeability. The feldspar dissolution by CO2 and organic acid is the primary formation mechanism of the effective reservoir in the Lingshui Formation, whereas the dissolution of glauconite is more common in the sandstone reservoirs of the Sanya and Meishan formations. [ABSTRACT FROM AUTHOR]

The transfer of carbon from land to the near-coastal ocean is increasingly being recognized in global carbon budgets. However, a more direct transfer of terrestrial carbon to the deep-sea is comparatively overlooked. Among systems that connect coastal to deep-sea environments, the Congo Submarine Canyon is of particular interest since the canyon head starts 30 km into the Congo River estuary, which delivers ~7 % of the total organic carbon from the world's rivers. However, carbon and sediment transport mechanisms that operate in the Congo Canyon, and submarine canyons more globally, are poorly constrained compared to rivers because monitoring of deep-sea canyons remains challenging. Using a novel array of acoustic instruments, sediment traps and cores, this study seeks to understand the hydrodynamic processes that control delivery of particulate organic carbon via the Congo Submarine Canyon to the deep-sea. We show that particulate organic carbon transport in the canyon-axis is modulated by two processes. First, we observe periods where the canyon dynamics are dominated by tides, which induce a background oscillatory flow (speeds of up to 0.15 m/s) through the water column, keeping muds in suspension, with a net upslope transport direction. Second, fast-moving (up to 8 m/s) turbidity currents occur for 35 % of the time during monitoring periods and transport both muddy and sandy particulate organic carbon at an estimated transit flux that is more than ten times the flux induced by tides. Remarkably, organic carbon transported and deposited in the submarine canyon has a similar isotopic composition to organic carbon in the Congo River, and in the deep-sea fan at 5 km of water depth. Episodic turbidity currents, together with background tidal currents thus promote efficient transfer of river-derived particulate organic carbon in the Congo Submarine Fan, leading to some of the highest terrestrial carbon preservation rates observed in marine sediments globally. [ABSTRACT FROM AUTHOR]

Tectonics play a significant role in shaping the morphology of submarine canyons, which form essential links in source-to-sink (S2S) systems. It is difficult, however, to investigate the resulting morphodynamics over the long term. For this purpose, we propose a novel experimental approach that can generate submarine canyons and hanging-wall fans on continuously evolving active faults. We utilize morphometric analysis and morphodynamic models to understand the response of these systems to fault slip rate (Vr) and inflow discharge (Q). Our research reveals several key findings. Firstly, the fault slip rate controls the merging speed of submarine canyons and hanging-wall fans, which in turn affects their quantity and spacing. Additionally, the long profile shapes of submarine canyons and hanging-wall fans can be decoupled into a gravity-dominated breaching process and an underflow-dominated diffusion process, which can be described using a constant-slope relationship and a morphodynamic diffusion model, respectively. Furthermore, both experimental and simulated submarine canyon–hanging-wall fan long profiles exhibit strong self-similarity, indicating that the long profiles are scale independent. The Hack's scaling relationship established through morphometric analyses serves as an important link between different scales in S2S systems, bridging laboratory-scale data to field-scale data and submarine-to-terrestrial relationships. Lastly, for deep-water sedimentary systems, we propose an empirical formula to estimate fan volume using canyon length, and the data from 26 worldwide S2S systems utilized for comparison show a strong agreement. Our geomorphic experiments provide a novel perspective for better understanding of the influence of tectonics on deep-water sedimentary processes. The scaling relationships and empirical formulas we have established aim to assist in estimating volume information that is difficult to obtain during long-term landscape evolution processes. [ABSTRACT FROM AUTHOR]

Subaquatic channels, situated in lakes, fjords, submarine canyons and on deep-sea fan systems, exhibit diverse morphometric characteristics controlled by sediment transport processes, particularly turbidity currents. These processes play a significant role in transporting sediment, organic carbon, nutrients, and pollutants and pose hazards to critical infrastructure. This study examines a balanced set of subaquatic channels across various settings, sizes, and locations, employing novel data harmonization techniques to address biases toward larger channels. The analysis reveals consistent scaling relationships, particularly the dominant role of bankfull width, influencing bankfull depth, cross-sectional area, wavelength, and amplitude. The aspect ratio (width-to-depth) emerges as a significant parameter, reflecting a necessary channel compactness to maintain turbidity currents. Meandering development reveals relations between width, wavelength, and amplitude, with a preference for specific ratios. Meandering is most pronounced at channel beginnings, transitioning to straighter forms downstream, potentially influenced by flow dynamics and flow confinement. The study broadens the understanding of subaquatic channel evolution, emphasizing the importance of bankfull width and providing insights applicable across settings and scales. [ABSTRACT FROM AUTHOR]

Submarine canyons enhance shelf-slope sediment exchange and influence hydrodynamic processes, with consequences for biogeochemical cycles. This work documents variations in the vertical export of biogenic matter on the northern shore of the Lower St. Lawrence Estuary (LSLE, Quebec, eastern Canada), which is characterized by the presence of an active submarine canyon system. A total of three moorings were deployed from November 2020 to September 2021. One nearshore mooring was deployed in the main axis of the Pointe-des-Monts (PDM) canyon system and was equipped with an Acoustic Doppler Current Profiler (ADCP), and two moorings equipped with sediment traps were deployed in the distal PDM canyon system and offshore Baie-Comeau (BC). The ADCP data revealed the occurrence of a minor sediment remobilization event (December 2020) and a small turbidity current (February 2021) in the canyon. Concurrent elevated fluxes of total particulate matter, particulate organic carbon, particulate nitrogen, and chloropigments showed that these events left a signature in the distal PDM sediment trap located >2.6 km further offshore. The composition of diatom and dinoflagellate assemblages was similar in the canyon system and offshore BC, but the diatom bloom occurred two weeks earlier (in mid-April) at the PDM site, where annual diatom and dinoflagellate fluxes were almost 2 times lower than at the BC site. A bloom of the potentially toxic diatom Pseudo-nitzschia seriata was also observed during the second half of September 2021 at the BC site. This study notably helps identify the relationship between near-bed canyon processes and biogenic matter export in the water column, thereby directly influencing the regional ecosystem. The study period further covered an anomalously nearly ice-free winter and thus, in the context of climate change, provides valuable insight into future trends of biogenic matter export in the LSLE. [ABSTRACT FROM AUTHOR]

The present study aims to investigate petrography characteristics and sedimental environments of upper Olenekian-middle Anisian deposits of Nakhlak group in the sedimentary-structural zone of central Iran. To this end, a section of these deposits with a thickness of 720 meters was first selected, and 190 samples were taken from this section for preparing thin sections. Also, quantitative and qualitative laboratory tests were performed and 25 samples of sandstone were selected for point counter analysis. The results indicated that the major deposits of this formation are related to siliciclastic, carbonate, and pyroclastic types, which are in the form of two facies associations. The facies association A at the bottom of the studied section with the thickness of 90 meters has a periodicity of clastic, carbonate, and pyroclastic facies. The clastic facies of this association consists of fine-grained sandstone. In addition, the carbonate facies in association A are characterized by two microfacies consisting of intraclast oolitic grainstone and oolitic grainstone. Further, tuffite is the only pyroclastic facies related to association A, which has a laminate structure, cross-bedding lamination, herringbone bedding, and upward-thinning and thickening cycles. The facies association, B which is deposited later, is more in the middle and top part of the section. The facies association B is 660 meters thick and has a periodicity of clastic and limestone facies. Clastic facies of this association includes four lithofacies such as conglomerate, pebble coarsegrained sandstone, medium-grained sandstone to thin layer siltstone and shale. The carbonate facies consists of four microfacies such as sandy intraclastic wackestone and mudstone. Furthermore, slumping structures, cross bedding, turbulence, boudinage structure, and convolute of sediments, along with the effects of erosional channels are observed in facies B. Field and laboratory studies conducted on this succession indicate the structure of facies association A was deposited in a mixed siliciclastic carbonate ramp. Finally, submarine canyons and submarine fan environments were left by increasing the depth of the facies association B in the deep part of sea and turbidity systems. [ABSTRACT FROM AUTHOR]

Here we show how ultra‐high resolution seabed mapping using new technology can help to understand processes that sculpt submarine canyons. Time‐lapse seafloor surveys were conducted in the axis of Monterey Canyon, ∼50 km from the canyon head (∼1,840 m water depth) over an 18‐month period. These surveys comprised 5‐cm resolution multibeam bathymetry, 1‐cm resolution lidar bathymetry, and 2‐mm resolution stereophotographic imagery. Bathymetry data reveal centimeter‐scale textures that would be undetectable by more traditional survey methods. Upward‐looking Acoustic Doppler Current Profilers at the site recorded the flow character of internal tides and the passage of three turbidity currents, while sediment cores collected from the site record flow deposits. Combined with flow and core data, the bathymetry shows how turbidity currents and internal tides modify the seabed. The turbidity currents drape sediment across the site, infilling bedform troughs and smoothing erosional features carved by the internal tides (e.g., rippled scours). Turbidity currents with speeds of 0.9–3.3 m/s failed to cause notable bedform movement, which is surprising given that flows with similar speeds produced rapid bedform migration elsewhere, including the upper Monterey Canyon. The lack of migration may be related to the character of the underlying substrate or indicate that turbidity currents at the site lack dense, near‐bed layers. The scale of scours produced by the internal tides (≤0.7 m/s) approaches the scale of features recorded in the ancient rock record. Thus, these results illustrate how the scale gap between seabed mapping technology and the rock record may eventually be bridged. Plain Language Summary: This study presents the highest resolution repeat seafloor mapping surveys to date in a submarine canyon. Centimeter‐scale seafloor surveys were conducted over an 18‐month period at a location ∼50 km from the head of Monterey Canyon. Turbidity currents (rapid, down‐slope density‐driven flows of water) and internal tides (tidal currents that flow along the seabed) were recorded by a seafloor instrument node deployed in the study area. Turbidity currents drape sediment across the bedforms, infill troughs, and smooth out erosional features carved by internal tides. While the turbidity currents caused considerable migration of bedforms in the upper canyon, there was surprisingly no notable migration at the study site. The lack of migration may be related to the relatively coarse nature of the seafloor underlying the bedforms and suggests that the turbidity currents at the site lacked a dense near‐bed layer characteristic of flows farther up‐canyon. The internal tides carved centimeter‐scale scours in the seabed, a scale that approaches that of features preserved in the rock record. This study, therefore, shows how new mapping technology may eventually bridge the scale gap between modern seafloor surveys and the ancient rock record. Key Points: Ultra‐high resolution time‐lapse mapping is combined with flow monitoring and sediment cores to document submarine canyon activityFast turbidity currents fail to cause notable bedform migration, though flows with similar speeds cause significant migration up‐canyonSub‐meter to meter‐scale scours, likely carved by internal tides, approach the scale of features preserved in the rock record [ABSTRACT FROM AUTHOR]

Enclosed depressions, termed pockmarks, are widespread seafloor morphologies, commonly associated with fluid seepage. This study provides the first detailed documentation of pockmarks offshore the South Westland margin of the South Island/Te Waipounamu, Aotearoa New Zealand. Pockmarks are identified from multibeam bathymetry (25-m grid) through manual and semi-automated selection in water depths of 100–2600 m. Pockmarks are most concentrated at 400–850 m water depth on continental slope areas between submarine canyons. A continuum of pockmark morphologies includes – (1) large (>0.5 km2 area) and irregularly shaped pockmarks above partially infilled channels; (2) small and circular pockmarks (∼100–200 m diameter; ∼0.008–0.03 km2 area) occurring between canyons; and (3) elongated and intermediate size pockmarks, generally oriented along-slope and often occurring above buried sediment waves. Elongated pockmarks appear to have been modified by near-seafloor oceanographic and/or turbidity current flows. Pockmark features occur across many locations around Aotearoa, including both the eastern and western margins. Some similar pockmark morphologies are identified in these different tectonic, sedimentary, and oceanographic settings, suggesting that there may be some similarity in formative mechanisms, but clear mechanisms leading to their formation remain enigmatic. [ABSTRACT FROM AUTHOR]

Submarine depressions are common features on the eastern Bahamian seafloor but the genesis of the deepest ones (>4000 m in water depth) is not well understood. We conducted a morphometric analysis and compared them to a worldwide database of rounded depressions, whatever their genesis is. The deep Bahamian depressions are large elongated structures, among the largest on Earth, with a width greater than 1000 m and a depth sometimes greater than 200 m. They extend at the toe of the Blake Bahama Escarpment (BBE), one of the tallest escarpments on Earth. Some of them align parallel to the BBE. Other depressions align along large submarine canyon axes. When aligned along canyon axes, the depressions closest to the canyon head are flanked by a topographic high interpreted as a slope-break deposit, i.e., sediment deposited after flow expansion following a hydraulic jump. Turbidity currents in the carbonate canyon system are not permanent processes, but are rather triggered during sea-level highstands when the carbonate platform is flooded. In addition, some depressions are not located in canyon axes. Consequently, the size and location of the depressions are not likely explained by a simple plunge pool mechanical erosion. Rather, our data suggest that all depressions could be initiated by giant karstic dissolution structures (dolines or sinkholes). Under interpretation, those located in canyon axes are sporadically refreshed by carbonate-laden turbidity currents. The height of the outsized chutes marking the crossing of the BBE by the canyon mouth generates a hydraulic jump allowing sediment deposition toward the bottom of the depression. Large depressions observed at this location in the Bahamas were the result of an initial dissolution phase related to retreat of the BBE and the more recent sediment-laden flow activity. The depressions orientated along canyon axes facilitated the regressive erosion that formed the canyons. At present, the depressions located at canyon mouths act as regular plunge pools. [ABSTRACT FROM AUTHOR]

Submarine canyons commonly occur on virtually all continental slopes. Their varied origins are widely studied but still debatable. Eastward (along-slope)–migrating submarine canyons, with nearly regular spacing, are well developed at the northern South China Sea. High-resolution three-dimensional seismic data show that these canyons are localized in the troughs between sediment waves. The waves were present on the slope since before ca. 10.5 Ma and were especially well developed during the late Miocene (ca. 10.5–5.5 Ma). This interval can be divided into two units, of which the upper unit (SU II) has larger sediment waves and much better-developed canyons compared to the lower unit (SU I). Submarine fans developed at the canyon mouths within SU II at the downdip termination of the confinement caused by the sediment waves. Gravity currents were captured between the waves, resulting in erosion mainly along the troughs between them. The canyons were forced to migrate eastward by the migration of the confining sediment waves. In this study, we present a new mechanism for the origin of such regularly spaced submarine canyons for the first time, which we attribute to the formation of regularly spaced sediment waves generated by contour currents. [ABSTRACT FROM AUTHOR]

The largest canyons on Earth occur on the seafloor, and seabed sediment flows called turbidity currents play a key role in carving these submarine canyons. However, the processes by which turbidity currents erode submarine canyons are very poorly documented and understood. Here we analyse the first detailed time-lapse bathymetric surveys of a large submarine canyon, and its continuation as a less-deeply incised channel. These are also the most comprehensive time-lapse surveys before and after a major canyon-channel flushing turbidity current. These unique field data come from the Congo Submarine Fan offshore West Africa, where canyon flushing turbidity currents between 2019 and 2020 eroded ~2.65 km3 of seabed sediment, as they travelled for over 1100 km at speeds of 5–8 m/s. This eroded sediment volume is equivalent to ~19–33 % of global sediment flux from all rivers to the oceans. The time-lapse surveys cover 40 % of the 1100 km long submarine canyon-channel. They show that erosion was predominantly (94 %) along the canyon-channel axis, with only 6 % from failures along canyon or channel flanks. However, erosion along the canyon-channel floor was very patchy; some areas were eroded to depths of 10–20 m, whilst intervening areas showed no significant change. Knickpoints with up-slope migrating headscarps account for 22 % of the total eroded volume. One knickpoint in the deep-sea channel migrated by 21 km in one year, making it the fastest moving submarine knickpoint yet documented. Most (62 %) eroded sediment was in zones extending across the canyon or channel floor, without distinct headscarps as is the case for knickpoints. Erosion restricted to outer bends only comprised 10 % of the total, suggesting processes of erosion differ significantly from meandering rivers in which outer bend erosion is more important. Patchy seabed erosion appears to be mainly due to flow-bed processes (e.g. knickpoints), but spatial variations in seabed sediment properties may also play a role. The irregular seabed erosion occurs despite near-uniform flow speeds observed between moorings and submarine cable breaks with spacing of tens to hundreds of kilometers. Patchy and localised erosion has important implications for assessing hazards to seabed telecommunication cables, which are more likely to break in areas of deep erosion, and for creating appropriate numerical models of seabed erosion and turbidity current behaviour, or how to interpretate ancient submarine canyons and channels in rock outcrops. • First detailed time-lapse surveys of a major submarine canyon-channel system. • Surveys capture patterns of erosion due to powerful canyon-channel flushing flows • Seabed erosion is highly localised and patchy, despite relatively uniform flow speed • Knickpoints can migrate at up to 21 km per year, but not all knickpoints migrated. • Localised erosion may explain why some seabed cables break, but others survive. [ABSTRACT FROM AUTHOR]

• Deep-sea habitats are typically food limited. • Stable carbon and nitrogen isotopes are useful tools to track food resources and trophic levels. • Isoscapes help track spatial variation in resource use across canyon and slope environments. • Deep-sea isoscapes provide avenue to understand shifting baselines with climate change. The deep sea is the largest biome on earth, but one of the least studied despite its critical role in global carbon cycling and climate buffering. Deep-sea organisms largely rely on particulate organic matter from the surface ocean for energy – these organisms in turn play critical roles in energy transport, transformation, storage, and sequestration of carbon. Within the deep sea, submarine canyons are amongst the most complex and dynamic environments in our oceans, where varied morphology, powerful currents, and variable nutrient conditions influence the distribution of species and transport of organic material throughout the water column and the seafloor. Significant habitat heterogeneity provides ideal substrates for cold-water corals, making submarine canyons of interest to conservation and management. However, how these and other topographic features in the deep ocean influence energy flow and trophic pathways is poorly known. Thus, submarine canyons serve as model systems to track variability in organic material flux and consequential utilization and assimilation by the benthos. In this study, we used an extensive stable isotope dataset to examine food-web structure in Baltimore and Norfolk submarine canyons and compared them to their adjacent slopes located along the U.S. Atlantic margin. Linear models were used to construct geospatially-explicit consumer isoscapes that predicted variation in carbon and nitrogen isotopes across the canyon-slope seascape, providing a predictive map from which to test hypotheses on the distribution and flow of energy resources, relevant to understanding whole community function. Communities were composed of isotopically diverse feeding groups with photosynthetically-derived organic carbon providing the basal food resource. Canyon communities were distinct from the slope, with canyon consumers significantly 13C-depleted, indicating a greater supply and/or utilization of fresh organic matter compared to the slope. Isoscapes for benthic and suspension feeders were distinct, possibly due to the consumption of different quality organic matter sources (fresh = suspension feeders, old = benthic feeders), each with distinct isotope composition. To our knowledge, our modeled isoscapes represent the first spatially extensive isotopic maps of deep-sea consumers, providing insights into regional-scale variation in stable carbon and nitrogen isotopes for different consumer groups. They provide a baseline for tracking climate-change induced fluctuations in the quality and availability of surface primary production and the consequential impact to benthic communities, which play critical roles in carbon cycling in our world's oceans. [ABSTRACT FROM AUTHOR]

Distal slope and basin depositional systems in deep waters of the Pará‐Maranhão Basin, Equatorial Brazil, are investigated using a high‐resolution 3D seismic volume, borehole data and multispectral satellite imagery. A Neogene calciclastic submarine fan and a series of channel‐levee systems are analysed at water depths of 100–3,500 m. Channel‐levee systems have sinuous and straight morphologies and are of different sizes. Their origin is related to turbidity flows sourced and funnelled from the carbonate shelf to submarine canyons and gullies, as well as from areas with marked slope instability. A mixed calciclastic‐siliciclastic sediment input is recognised with autochthonous calcarenites and calcilutites comprising the bulk of sediment on the mid and outer continental shelf. Minor amounts of siliciclastic sediment sourced from small rivers occur on the inner shelf. Sedimentation processes of a distally steepened carbonate ramp are discussed considering a general depositional setting dominated by fluctuations in relative sea‐level. Cross‐sectional and planar parameters of mixed calciclastic‐siliciclastic channel‐levee systems are compared to their siliciclastic counterparts. Morphological results show similarities between calciclastic and siliciclastic channel‐levee systems. As a corollary, three types of channel‐levee systems are described: (a) channels related to calciclastic submarine fans, (b) low‐sinuosity, aggradational channels, and (c) high‐sinuosity channels. [ABSTRACT FROM AUTHOR]

The North Palawan Canyon is a large, previously undescribed submarine canyon that incises the continental shelf and slope of the southern South China Sea. Using multibeam bathymetric data and two-dimensional seismic reflection data, we have characterized current canyon morphology and documented lower-canyon migration in cross-section since the middle Miocene. We have also explored possible causes for the ancient migrations. The 175 km modern canyon is flanked by sediment waves outside its northern bank, and depositional lobes fan out from the canyon mouth. Over the past 15 million years, at least 20 cycles of significant canyon incising and infilling have occurred, along with significant canyon migration. This migration, as recorded in the sedimentary (seismic) record near a leftward bend in the canyon's lower reach, can be divided into three stages: southward migration during the middle Miocene (averaging 1.24 km/m.y.), northward migration during the late Miocene (1.34 km/m.y.), and stationarity since the Pliocene. The overall zigzagging pattern of the canyon thalweg (as seen in cross-section through time) results from lateral and downstream migration in an aggradational environment. The early (middle to late Miocene) rapid zigzagging migration of the lower main channel, first southward and then northward, was probably associated with the strong collision of the North Palawan Block with the Philippine Mobile Belt, which would have triggered submarine instabilities and deformed the seafloor. The more recent (Pliocene and later) slowing or cessation of canyon migration is likely the result of the now quieter tectonic setting and long-term climatic cooling and drying. [ABSTRACT FROM AUTHOR]

How and when sediment moves from shallow marine to deep-water environments is an important and poorly understood control on basin-scale sediment dispersal patterns, the evolution of continental margins, and hydrocarbon exploration in deep-water basins. The Golo River (Eastern Corsica, France), its delta, canyons, and fans provide a unique opportunity to study sediment routing from source to sink in a relatively compact depositional system. We studied this system using an array of high-frequency seismic data, multi-beam bathymetry, and five cores for lithology and age control. Movement of sediment to deep water was controlled by interactions between the Golo River, the Golo Delta, and shelf-penetrating submarine canyons. Sediment moved to deep water when lobes of the Golo Delta prograded to the heads of these canyons, or when the Golo River itself flowed directly into one of them. Sand accumulated in canyons, deep-water channels, and submarine fans during glacial periods of low sea level, while mud was deposited throughout the slope, in the relatively short reach of leveed-confined channels, and in the mud-rich fringes around the sandy fans. During interglacial periods of high sea level, the basin was blanketed by mud-rich deposits up to 10 m thick interbedded with distinctive carbonate-rich sediments. Deposition rates in the basin ranged from 0.07 m/ka to 0.59 m/ka over the last 450 ka. Mud deposition rates remained relatively constant at ~0.16 m/ka during all time periods, while sand deposition only happened during glacial periods of low sea level with an average rate of 0.24 m/ka. In addition to sea-level controls on sediment delivery, avulsions of the Golo River and its deltaic lobes preferentially routed sediment down either the North or South Golo canyons. Thus, while the larger, sequencescale architecture of the basin is controlled by allogenic sea level forcing, millennial-scale autogenic processes operating on the shelf and in deep water shaped the distribution of sand and mud, and the internal geometry of the deltas and submarine fans that they fed. While some aspects of the Golo system are characteristic of steep, tectonically active margins, others such as the nature of connections between rivers and shelf-penetrating submarine canyons are observed in most margins with active submarine fans regardless of their tectonic setting. [ABSTRACT FROM AUTHOR]

Six submarine canyons are distributed along the active margin off SW Taiwan. Using multi-beam bathymetric data and reflection seismic profiles to determine canyon head locations with respect to shelf edge, five of these canyons were classified into the following three types: 1. river-connected; 2. shelf-indenting; and 3. slope-confined. The remaining canyon was re-interpreted as a sea valley. Type 1 canyon, the Kaoping Canyon, is directly connected to the Kaoping River and supplied with terrestrial sediment. The canyon head segment tends to generate hyperpycnal flows during flooding, causing intense erosion of seafloor across the shelf and slope and forming a major sediment conduit. The Penghu, Kaohsiung and Fangliao canyons are of type 2 and incise into the shelf, forming a V-shaped head segment with abundant slumping features. Without continuous sediment supply from rivers, the canyon head receives sediments mainly from local slope failures on canyon walls and is unable to generate intense erosive sediment flows, resulting in an indentation into the shelf over a short distance. Oceanographic/hydrodynamic measurements close to the canyons are still not available for the region, despite they could shed light on the on-going sediment dynamics in the area. The Shoushan Canyon is a type 3 canyon characterized by limited sediment input from the Kaoping Shelf and weak canyon erosion, especially during sea-level highstands, resulting in a relatively straight canyon course confined to the upper slope. These submarine canyons share common regional tectonics, sea-level changes and climatic conditions. However, they evolved via local processes mainly controlled by sediment input directly related to head location, resulting in distinct morphologies and sizes. These canyons have remained active during the present-day sea-level highstand. Frequent earthquake and flooding events are the major triggering factors for sediment failures and generation of subsequent turbidity currents, resulting in substantial incision into the canyon. The results of the present study indicate that the SW Taiwan margin is characterized by canyons of type 1 and type 2 (n = 4) with only one type 3 canyon. This represents large percentages of type 1 and type 2 canyons compared to other regions of the world. Narrow shelf and abundant sediment supply are the two main controls for the presence of river-connecting and shelf-incising canyons on the active Taiwan margin. [ABSTRACT FROM AUTHOR]

The monitoring of turbidity currents enables accurate internal structure and timing of these flows to be understood. Without monitoring, triggers of turbidity currents often remain hypothetical and are inferred from sedimentary structures of deposits and their age. In this study, the bottom currents within 20 m of the seabed in one of the Pointe‐des‐Monts (Gulf of St. Lawrence, eastern Canada) submarine canyons were monitored for two consecutive years using Acoustic Doppler Current Profilers. In addition, multibeam bathymetric surveys were carried out during deployment of the Acoustic Doppler Current Profilers and recovery operations. These new surveys, along with previous multibeam surveys carried out over the last decade, revealed that crescentic bedforms have migrated upslope by about 20 to 40 m since 2007, despite the limited supply of sediment on the shelf or river inflow in the region. During the winter of 2017, two turbidity currents with velocities reaching 0·5 m sec−1 and 2·0 m sec−1, respectively, were recorded and were responsible for the rapid (<1 min) upstream migration of crescentic bedforms measured between the autumn surveys of 2016 and 2017. The 200 kg (in water) mooring was also displaced 10 m down‐canyon, up the stoss side of a bedform, suggesting that a dense basal layer could be driving the flow during the first minute of the event. Two other weaker turbidity currents with speeds <0·5 m sec−1 occurred, but did not lead to any significant change on the seabed. These four turbidity currents coincided with strong and sustained wind speed >60 km h−1 and higher than normal wave heights. Repeat seabed mapping suggests that the turbidity currents cannot be attributed to a canyon‐wall slope failure. Rather, sustained windstorms triggered turbidity currents either by remobilizing limited volumes of sediment on the shelf or by resuspending sediment in the canyon head. Turbidity currents can thus be triggered when the sediment volume available is limited, likely by eroding and incorporating canyon thalweg sediment in the flow, thereby igniting the flow. This process appears to be particularly important for the generation of turbidity currents capable of eroding the lee side of upslope migrating bedforms in sediment‐starved environments and might have wider implications for the activity of submarine canyons worldwide. In addition, this study suggests that a large external trigger (in this case storms) is required to initiate turbidity currents in sediment‐starved environments, which contrasts with supply‐dominated environments where turbidity currents are sometimes recorded without a clear triggering mechanism. [ABSTRACT FROM AUTHOR]

The article presents a detailed analysis of the underwater morphology of the entire Black Sea basin beyond the shelf break. The focus is on submarine valley systems on continental slope and rise zones, and partially in the abyssal plain area. The present research is among the very few studies that have undertaken a morphological analysis on a regional scale, for an entire marine basin. This achievement was possible by using the publicly available EMODnet bathymetric map of the Black Sea. The Black Sea submarine valleys networks are presented in a map-sketch. It includes 25 valley systems, 5 groups of simple first order channels, and other number of simple, not associated channels. The 25 valley systems are adding up more than 110 main channels and tributaries. Morphological description and analysis of each of the mapped systems is given – shape and plan view morphology, dimensions (length and surface) and slope gradient. Some considerations about the amount of sediments supplied by the valleys from the shelf to the basin floor, forming the deep-sea fans, are presented. For a more detailed and precise image of the Black Sea network of submarine valleys additional work would be necessary to cover the entire basin with a minimum standard network of modern bathymetric mapping and of high resolution seismic survey lines. To take into account the composition and geological structure of different sectors, as factors that influence significantly the morphology of the seabed, would be also particularly useful. [ABSTRACT FROM AUTHOR]

Repeat multibeam bathymetric surveys conducted in 2004, 2005 and 2018 show that seven slope-confined canyons on the continental slope of the Pearl River Mouth Basin, South China Sea, were dominated by large volume, widespread erosion. Erosion volumes were up to 3.4 times greater than deposition volumes. Erosion-dominated areas of the canyons are up to 2.3 times greater than areas dominated by deposition. Average rates of erosion (ranging from 0.7 to 0.8 m/yr) were greater than average rates of deposition (ranging from 0.5 to 0.8 m/yr). In plan view, the erosion-dominated zones exhibit two characteristic shapes: (1) linear, found mainly in upper canyon reaches, distributed predominantly along canyon axes and at the base of eastern canyon walls, and; (2) blocky, found mainly in lower canyon reaches, widely distributed along the steep canyon walls and on lower-canyon interfluves. The deposition-dominated zones are scattered along canyon floors and walls. Seismic reflection data show lateral shifts of canyon fill deposits through time, indicative of longer-term eastward canyon migration. The linear erosion-dominated zones may be attributed to erosive turbidity currents triggered by energetic internal solitary waves shoaling on the shelf. The eastward canyon shifts were likely induced by rapid near-bed eastward currents generated mainly by westward propagating powerful internal solitary waves of depression. The widespread erosion in the deeper canyon areas and interfluves is likely a consequence of slope instabilities associated with the presence of gas hydrates. This study indicates that active sedimentary processes can occur in slope-confined canyons even during sea level highstands. Local, site-specific oceanographic and geological features (e.g., internal solitary waves, gas hydrates) can significantly increase sedimentary activity in and around submarine canyons. • Seven slope-confined canyons in the northern South China Sea were dominated by erosion, 2004–2018 • Ratios of erosion-dominated to deposition-dominated area in the canyons ranged from 1 to 2.3 • Ratios of eroded to deposited sediment volumes ranged from 1.2 to 3.4 • In the upper canyon reaches, internal solitary waves resulted in the triggering of turbidity currents. • In the lower reaches, gas hydrate activity likely caused submarine slope instabilities. [ABSTRACT FROM AUTHOR]

Convergent margins host more than half of all global submarine canyons. In this environment, the lack of cognition of the canyon morphology variation and their controls in two different types of marine forearcs (erosive and accretionary) remains exists. Based on shipborne bathymetric maps, we systematically analyze width, incision depth and slope gradient of 17 submarine canyons along the Chilean marine forearc. We divide the study area into an erosive northern area, a transitional central area, and an accretionary southern area based on trench sediment cover and in line with previous tectonic interpretations. In the northern and central areas, limited sediment supply and little erosion from infrequent turbidity currents form narrow and shallow canyons that arrive at the toe of margin. Subduction erosion contributes to a simple and regular slope morphology where regional subsidence and trench-parallel faulting activities lead to vertical crustal movement and a steep thalweg of canyons' lower reach. In contrast, frequent canyon flushing/filling turbidity currents and slope failures on the canyon walls result in a wider range of canyon width and incision depth in the south. Here, the formation of an accretionary prism generates fold and thrust ridges at the seafloor that reduce the slope gradient of canyons' lower reach. Canyon morphology within the prism region has a larger range than the non-prism (backstop) region due to the higher erodibility of the less consolidated sediment. In addition, convex-up step-shaped bedforms develop along 14 canyon thalwegs, also suggesting regional uplift/subsidence and normal faulting in the north and central region but folding and thrust faulting in the south. This work not only reveals the difference of canyon morphology on active marine forearcs but also may help to understand controls on submarine canyon morphologies along the Chilean margin as well as in other convergent margins. • 17 large submarine canyons are identified and investigated along the Chilean margin. • Submarine landslides and turbidity currents widen and deepen canyons. • Subsidence and normal faults caused by subduction erosion steepen canyons thalwegs. • Canyon morphology has a larger range within accretionary prism due to sediment accretion. • Step-shaped bedforms along canyon thalwegs reflect localized uplift/subsidence and folds/thrust faults. [ABSTRACT FROM AUTHOR]

Submarine fans are ubiquitous in modern deep-water environments. Such systems reported in the literature are largely fed by shelf-indented canyons receiving ample fluvial or longshore drift sediment inputs, whereas those nourished by slope-confined canyons far away from terrigenous sediment sources remain poorly understood. Herein, we report such a system, the Yitong submarine canyons – fan apron system (YCFS), from the northern South China Sea. This system was studied using multibeam bathymetric and two-dimensional multichannel seismic data, combined with geological constraints from nearby International Ocean Discovery Program drilling sites. YCFS consists of approximately 12 submarine canyons confined in the lower continental slope of >1200 m water depth, which feed a fan apron in the connecting abyssal plain. The canyons are erosion-dominated, as evidenced by their V-shaped cross-sections with up to 708 m deep incisions. Canyon infillings comprise mass transport deposits and turbidites, and interfluves exhibit features such as landslides, creep-typed sediment waves, and gullies, indicating the canyons and interfluves are dominated by mass transport and turbidity-current processes. The fan apron is generally depositional, in which channels and channel-levee complexes, turbidite lobes, and mass transport deposits comprise the main depositional elements. In the canyon-to-fan transitions, supercritical turbidity current features and bedforms, including plunge pools and connected sediment mounds, cyclic steps, and antidunes, are developed, which are linked to the deceleration and hydraulic-jump effects of the high-velocity turbidity currents shedding off the canyons. Seismic stratigraphic analysis revealed that YCFS was initiated in Late Miocene. The formation and maintenance of YCFS are linked to the long-term existence of an upslope margin-parallel basement high. The latter could have maintained a steep slope condition (up to 6.5°) that favors the development of canyons and supercritical turbidity currents. Because of the blocking effect of the basement high , YCFS receives limited supply of the shallow-water sediments. • A deep-sea fan apron fed by slope-confined canyons lacks ample land-based supply. • Developed supercritical-flow bedforms indicate high-energy fan apron environments. • Tectonism plays a critical role in the development of the system. [ABSTRACT FROM AUTHOR]

The article focuses on the initiation and evolution of unidirectionally migrating deep-water channels (UCs) and challenges the interpretation of bottom-current sediment waves as the controlling factor. Topics include discrepancies in the morphology, architecture, and migration patterns of seismic facies associated with UCs compared to recognized criteria for bottom-current sediment waves; and development of UCs are influenced by interactions between turbidity and bottom-current sediment waves.

The presently active region of the Congo deep-sea fan (around 330,000 km 2 ), called the terminal lobes or lobe complex, covers an area of 2500 km 2 at 4700–5100 m water depth and 750–800 km offshore. It is a unique sedimentary area in the world ocean fed by a submarine canyon and a channel-levee system which presently deliver large amounts of organic carbon originating from the Congo River by turbidity currents. This particularity is due to the deep incision of the shelf by the Congo canyon, up to 30 km into the estuary, which funnels the Congo River sediments into the deep-sea. The connection between the river and the canyon is unique for major world rivers. In 2011, two cruises (WACS leg 2 and Congolobe) were conducted to simultaneously investigate the geology, organic and inorganic geochemistry, and micro- and macro-biology of the terminal lobes of the Congo deep-sea fan. Using this multidisciplinary approach, the morpho-sedimentary features of the lobes were characterized along with the origin and reactivity of organic matter, the recycling and burial of biogenic compounds, the diversity and function of bacterial and archaeal communities within the sediment, and the biodiversity and functioning of the faunal assemblages on the seafloor. Six different sites were selected for this study: Four distributed along the active channel from the lobe complex entrance to the outer rim of the sediment deposition zone, and two positioned cross-axis and at increasing distance from the active channel, thus providing a gradient in turbidite particle delivery and sediment age. This paper aims to provide the general context of this multidisciplinary study. It describes the general features of the site and the overall sampling strategy and provides the initial habitat observations to guide the other in-depth investigations presented in this special issue. Detailed bathymetry of each sampling site using 0.1–1 m resolution multibeam obtained with a remotely operated vehicle (ROV) shows progressive widening and smoothing of the channel-levees with increasing depth and reveals a complex morphology with channel bifurcations, erosional features and massive deposits. Dense ecosystems surveyed in the study area gather high density clusters of two large-sized species of symbiotic Vesicomyidae bivalves and microbial mats. These assemblages, which are rarely observed in sedimentary zones, resemble those based on chemosynthesis at cold-seep sites, such as the active pockmarks encountered along the Congo margin, and share with these sites the dominant vesicomyid species Christineconcha regab . Sedimentation rates estimated in the lobe complex range between 0.5 and 10 cm yr −1 , which is 2–3 orders of magnitude higher than values generally encountered at abyssal depths. The bathymetry, faunal assemblages and sedimentation rates make the Congo lobe complex a highly peculiar deep-sea habitat driven by high inputs of terrigenous material delivered by the Congo channel-levee system. [ABSTRACT FROM AUTHOR]

The complex topography of submarine canyons may result in different composition of benthic foraminifera assemblages. To understand how trophic, hydrological and sedimentological conditions in submarine canyons can influence the distribution of benthic foraminifera, and to use this information to corroborate paleoenvironmental interpretations for the Holocene, we investigated recent benthic foraminiferal assemblages (total fauna >63 μm) and sedimentological data in two canyons (CANWN and CAND) in the Espírito Santo Basin (ESB) between 18°20′ and 21°20′ S. Surface sediment samples (0–2 cm) were collected inside the canyons (150 to 1300 m water depth) and in shelf-slope adjacent transects (50 to 1300 m water depth). The density, taxonomic diversity, and assemblage composition of benthic foraminifera change with depth and location. The distinct ecological preferences of the most abundant taxa allowed us to recognize five benthic foraminiferal groups. Three groups (V, III, and I) are present in different bathymetric sectors; Group V: outer shelf (50 m), Group III: upper, and middle – lower slope (150 to 400 m), and Group I: middle – lower slope (1000 to 1300 m). Groups II and IV show no characteristic bathymetric distribution and are present only in CAND and in CANWN, respectively. Group V consists of Hanzawaia boueana , Peneroplis planatus , and Quinqueloculina lamarckiana; Group III is dominated by Globocassidulina rossensis and Trifarina spp.; Group I consists of Globocassidulina crassa , Bolivina lowmani , Gavelinopsis versiformis , Alabaminella weddellensis , and Epistominella exigua. The main species in Group II (CAND, 150, 1000 to 1300 m) are Trifarina angulosa , Globocassidulina subglobosa , and Discorbis vilardeboanus. Group IV (middle – lower CANWN, 1000 to 1300 m), consists mainly of agglutinated species Glomospira charoides , Rhabdammina abyssorum , and Psammosphaera fusca. Our data suggest that the quantity (and quality) of food supply, hydrodynamic conditions and sediment properties are the main drivers controlling the bathymetric distribution of benthic foraminiferal assemblages in both canyons. The middle – lower CANNW revealed unstable trophic conditions, related to terrigenous sediment input due to turbidity currents. In CAND, the foraminiferal assemblages ecology indicated sufficient organic matter supply that favors species establishment and diversity, indicating a more productive and less unstable environment than in CANWN. • Environmental factors related to submarine canyons influence the benthic foraminiferal distribution. • CANWN and CAND assemblages are different from the open slope. • The agglutinated assemblage in the middle-lower CANWN may reflects a mass-transport movement. • Benthic foraminiferal species abundance indicated enough organic matter trapped within CAND. [ABSTRACT FROM AUTHOR]

To improve our understanding and management of marine plastic pollution of the ocean, a total plastic budget is needed which quantifies the sources and sinks, as well as inputs and removal of plastic per unit time. The current state of knowledge indicates that the coastal zone and ocean water column are major locations for plastic pollution, but the fate of much of this must ultimately be the deep ocean floor. We reviewed 23 journal articles that provide 280 observations of deep-sea sediment microplastic concentration across six different off-shelf environments. We calculate the following mean concentrations of microplastic particles (number) per kg of sediment: continental slope 502; submarine canyons 784; submarine fans and continental rise 714; abyssal plains 217; trenches and troughs 2782; and abyssal hills, mountains and other ocean floor 165 particles kg−1. These figures are alarming because several exceed one estimate of 'safe' levels of microplastic concentration for benthic marine life (540 particles kg−1). Monitoring of the concentration of plastic particles in sediments of submarine canyons, fans and continental rise environments and in trenches and troughs should be a priority to ensure efficacy of policies and actions taken to curb ocean plastic pollution at both the national and global level. We estimate 3.05 million tonnes of microplastic resides in deep ocean sediments but acknowledge the uncertainties of this figure. If correct, this figure implies that the ocean water column (which may contain as much as 90 million tonnes of microplastic) is a major, transitory sink for MP, forming a suspended, marine plastic cloud. In addition to particle concentrations, further measurements of the size and mass of microplastic in deep-sea sediments and in the water column are needed to advance development of mass balance budgets for marine plastic pollution. • Estimated mass of microplastic in global seafloor sediments is 3.05 million tonnes • Small plastic mass in sediments is consistent with a suspended marine plastic cloud • Microplastic content in sediments exceeds 'safe' levels for benthos in many habitats • Prioritise monitoring to ensure efficacy of policies to curb plastic pollution [ABSTRACT FROM AUTHOR]

Up to date, most in-situ studies and observations of turbidity currents were conducted in submarine canyons that are either, large, shelf incising or adjacent to big perennial rivers, or a combination of these features. Little if any observations have been made in the numerous, small submarine canyons (<20 km) that are confined to the continental slope and located far offshore smaller and often ephemeral streams, which are far more common globally. In this study, measurements were collected from October 2019 until June 2020 in Bat-Galim Canyon, a small (5 km long) submarine canyon located offshore Haifa, Israel, in the Eastern Levantine Basin (southeastern Mediterranean) where only minor, ephemeral streams reach the sea. This was performed using two similar mooring stations, positioned at depths of 350 and 710-meter along the canyon, which carried an array of measuring instruments, set between 2 and 50 meters above the canyon thalweg. Our data shows that the small Bat-Galim canyon is an active conduit for significant sediment transport to the deep-sea, much of it via turbidity currents that flow down the canyon during winter storms. The characteristic values of the turbidity currents in the Bat-Galim canyon were similar to those reported in much bigger submarine canyons. In addition, we observed temperature inversions during these events, wherein the sediment-laden warm surface water plunged and flowed underneath the colder, and otherwise denser, canyon water. This temperature inversion may lead to sediment lofting and upward convection through the water column for hundreds of meters, once sediment settling relieves the warm water of some of its ballast. These unique findings highlight the need to investigate the importance of small submarine canyons on continental slopes worldwide as water and sediment conduits to the deep-sea, even in dryer regions, and the impact of temperature inversions by turbidity currents on various water column processes. • First time-series measurements within a submarine canyon in the Levantine Basin. • Turbidity currents observed in the small (5km long) and confined to the slope canyon. • Similar traits of turbidity currents and sediment transport in this and much larger, shelf-incising canyons. • These winter events caused temperature inversions in the water column. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fatty acids in Congo lobe sediments are mainly of terrestrial origin. • Soil OM is distributed homogenously and plant debris heterogeneously. • Small amounts of biomarkers from phytoplankton reach the terminal lobe complex. • Oxic degradation is limited to the topmost surface sediments. • Long chain fatty acids are preserved in turbidite deposits over millennia. The Congo River is connected to its submarine canyon and supplies large quantities of terrestrial organic carbon via powerful turbiditic currents down to the Congo deep-sea fan. We investigated sediment cores from the terminal lobe complex of the Congo deep-sea fan (∼750 km offshore, ∼5000 m water depth), in order to assess the value of fatty acid biomarkers as indicators of organic matter (OM) origin and processes affecting its distribution and preservation in recent turbidites. Sediments from the Congo deep-sea fan are enriched in fatty acids compared to the surrounding abyssal plains and their composition closely resembles that of sediments recovered in the Congo River. Long chain fatty acid (LCFA) biomarkers in conjunction with the branched vs isoprenoid tetraether index (BIT) show that OM mostly originates from soil erosion and continental higher plants. This material has undergone limited reprocessing during transit certainly due to tight interactions with mineral particles and rapid transfer. The presence of phytoplankton biomarkers at the entrance of the terminal lobe area highlights that inputs of fresh OM, albeit limited, can reach the lobe complex. By combining fatty acid profiles and geochemical proxies in a multivariate analysis, we highlight that OM degradation is mostly limited to the oxic layer, and that fine soil-derived particles and the coarser higher plant detritus display distinct depositional dynamics. Finally, LCFA are remarkably well preserved under anoxic conditions at different time scales, in recent turbidites deposited during the last century and those deposited several thousand years ago. [ABSTRACT FROM AUTHOR]

[Display omitted] • The submarine canyons mainly began to develop during the last glacial maximum (LGM), and some might initiate earlier in the early Pleistocene (<1.8 Ma) and further evolved after the LGM. • The slope failure (mass transport) induced by gas hydrate dissociation and associated methane seepage during the glacial epoch (mainly the LGM) is proposed as the main controlling factor for canyon initiation. • A coupled model was established to illustrate the four evolutional stages of the submarine canyons responsing to gas hydrate system. Submarine canyons serve as conduits to transport terrigenous detrital sediment and organic carbon to the deep sea. Herein, we carried out a detailed analysis of the geomorphological and erosional-depositional features of submarine canyons on the middle and southern slopes of the Okinawa Trough based on the established isochronous chronostratigraphic framework. According to sequence stratigraphy and well-seismic calibration technologies, the ages of six stratigraphic boundaries are redetermined, which are aged: Seafloor (0 Ma), T LGM (23kyr B. P.), T 0 (1.8 Ma), T 10 (6.0 Ma), T 12 (11.02 Ma), and T 16 (16.12 Ma), respectively. The submarine canyons mainly began to develop during the last glacial maximum (LGM), and some might initiate earlier in the early Pleistocene (<1.8 Ma) and further evolved after the LGM. Along the axial direction, the heads of these shelf-indenting canyons were mostly inherited from the ancient incised valleys developed on the shelf edge during the LGM; and the canyon channels were filled with multi-stage turbidites and mass transport deposits (MTDs). The multi-BSRs (bottom simulating reflectors), arched or imbricated and chaotic or twisty reflections, as well as pipe, notch, and mud volcano structures on seismic profiles indicate widespread gas-bearing fluid migration and methane seepage that is possibly related to gas hydrate dissociation. Besides the sea-level change and tectonic movements, we find that the slope failure (gravity flow) induced by gas hydrate dissociation accompanied by methane seepage during the glacial epoch (mainly the LGM) is a main controlling factor for canyon initiation in the Okinawa Trough. The link between canyon development and methane seepage is confirmed by characteristic seismogeologic expressions, such as the MTDs associated with BSRs, the imbricated, twisty or chaotic seismic reflections inside the MTDs, the liquefaction deformation structures, and the fluid transport pipes. In addition, the notches (maybe pockmarks or seabed depressions) that indicate methane escaping on the canyon sidewalls, and the truncated relationship between the BSRs and canyon channels further indicate that there is a complex relationship between the submarine canyons and the methane seepage associated with gas hydrate. Finally, a coupled model was established to illustrate the four evolutional stages of the submarine canyons, which provide an attractive case of how the submarine canyon dynamically responds to gas hydrate system. Therefore, our new findings are of great significance for understanding the mechanism of the submarine canyon and reconstructing the evolutionary history of gas hydrate modulated by sea-level changes in geological history. [ABSTRACT FROM AUTHOR]

Deep sea channel systems are recognized in most submarine fans worldwide as well as in the geological record. The Indus Fan is the second largest modern submarine fan, having a well-developed active canyon and deep sea channel system. Previous studies from the upper Indus Fan have reported several active channel systems. In the present study, deep sea channel systems were identified within the middle Indus Fan using high resolution multibeam bathymetric data. Prominent morphological features within the survey block include the Raman Seamount and Laxmi Ridge. The origin of the newly discovered channels in the middle fan has been inferred using medium resolution satellite bathymetry data. Interpretation of new data shows that the highly sinuous deep sea channel systems also extend to the east of Laxmi Ridge, as well as to the west of Laxmi Ridge, as previously reported. A decrease in sinuosity southward can be attributed to the morphological constraints imposed by the elevated features. These findings have significance in determining the pathways for active sediment transport systems, as well as their source characterization. The geometry suggests a series of punctuated avulsion events leading to the present array of disconnected channels. Such channels have affected the Laxmi Basin since the Pliocene and are responsible for reworking older fan sediments, resulting in loss of the original erosional signature supplied from the river mouth. This implies that distal fan sediments have experienced significant signal shredding and may not represent the erosion and weathering conditions within the onshore basin at the time of sedimentation. [ABSTRACT FROM AUTHOR]

The Sohar Basin, located offshore the East Coast of the Arabian Peninsula, is an area that has seldom been the focus of international oil companies. While all commercial discoveries in the UAE and Oman have been made to the west and south of the Oman Mountains, the Sohar Basin is underexplored and remains prospective. This lack of activity is primarily because the Thamama reservoir, which has yielded huge success to the west of the Oman Mountains is likely not present within the Sohar Basin. However, potential traps, reservoirs, and source rocks are present within the Tertiary succession. The Sohar Basin formed in the late Cretaceous after the obduction of the Semail Ophiolite onto the Arabian Plate. Following a period of tectonic quiescence, which lasted until the Early Eocene, the gravitational collapse occurred along the eastern edge of the present-day Oman Mountains. Interpretation of both 2D and 3D seismic reveals that the subsurface is comprised of three tectonostratigraphic units, defined as pre-, syn-, and post-tectonic packages. North-South trending thrust faults generate distinct mini-basins within the pre- and syn-tectonic sequences. The post-tectonic sequence is defined by the development of prograding systems in a tectonically quiescent margin formed in the Lower Miocene and which persists to the present day. Deep-water depositional systems dominate the undrilled far-east and south of the basin where the presence of submarine canyon systems and associated basin floor fans is supported by 3D seismic data. In recent times, the Sohar Basin has been subject to extensional faulting likely driven by sediment load caused by a prograding delta system. The results of this work reveal that multiple untested play types exist within the Sohar Basin, which are comprised of both structural and stratigraphic elements. This paper integrates both a structural and sequence stratigraphic interpretation to provide insights into the tectonostratigraphic evolution of the Sohar Basin. Consequently, the fundamentals of play fairway mapping have been employed to unlock the hydrocarbon prospectivity offshore the UAE's East Coast. • A sequence stratigraphic approach unlocks the prospectivity in the Sohar Basin, offshore the east coast of the UAE. • Untapped prospectivity lies within deep marine turbidities within the Northern Sohar Basin. • Toe thrust systems have developed in response to post orogenic collapse of the Hajar Mountains. • A passive continental margin developed during the Miocene within the Northern Sohar Basin. [ABSTRACT FROM AUTHOR]

The 2016 Mw 7.8 Kaikōura Earthquake triggered simultaneous turbidity currents down ten submarine canyons along a 200 km stretch of the continental slope, east of New Zealand. They discharged into the abyssal Hikurangi Channel which flows >1500 km northwards along the trench floor as part of the Hikurangi Subduction Margin. One hundred and thirty-six foraminiferal samples from the 2016 turbidites and pre-turbidite sediment from 25 canyon/channel cores, collected during surveys 3 days, 2.5 and 8 months after the event, were used to provide insights into the complexities of these submarine gravity flows. Transport in the turbidity currents produced no significant additional breakage of foraminiferal tests, even when transported 650 km down channel. We conclude that highly variable planktic foraminiferal fragmentation index (FI) values indicate that test breakage in turbidite samples is primarily inherited from dissolution on the seafloor at their source area, which is often anomalously high because of lowered sediment pH as a result of the breakdown of the high organic carbon flux. All turbidite and pre-turbidite faunas have strong signatures of downslope displacement (presence of shallow-water benthics, size-sorted test distributions, low percentage of planktics). This is not surprising as all cores were taken in the canyon or channel floor pathways to collect turbidite sequences, with turbidity flows estimated to have a recurrence time of ∼150 yrs. Pre-turbidite faunas can be distinguished from the 2016 turbidites' faunas by having greater percentage of planktics and lower ratios of shallow to deep benthic tests (S/D Index). 210Pb profiles show that the laminated pre-turbidite sediment accumulated slowly and the foraminiferal content indicates it is composed of reworked earlier turbidite sediment with the addition of contemporaneous deep-water benthic tests and the rain of planktic tests mixed in. There are no consistent trends in any foraminiferal faunal parameters with distance displaced in the turbidity current (10–650 km). Rather, intra-turbidite (10–75 cm thick) faunal variability in a single core is often considerable and is attributed to erosion and entrainment of deep-seafloor tests by the passage of turbulent turbidity current heads, variable source canyon depths, different source canyon provenances, and test-size sorting during transport and deposition resulting in vertical and longitudinal fractionation of the smallest tests and finest sediment. This study suggests that a single foraminiferal fauna is often, but not always, insufficient to characterise a turbidite or for use in correlation with turbidites in other cores or exposures. • Foraminiferal tests showed little breakage during 650 km of turbidite transport. • Intra-turbidite foraminiferal variability is often considerable. • Turbidity currents sometimes erode and entrain deep-seafloor foraminifera. • Foraminiferal faunas can identify different turbidite provenance areas. [ABSTRACT FROM AUTHOR]

Submarine canyons are prevalent in the world's oceans and are instrumental in transporting sediment from coastal regions to deep-sea fans. Conventional sediment parameters such as mean grain size, sorting, and provenance have typically been used to characterize these deposits, but they provide little information on sediment source or the delivery processes involved. Fortunately, transported along with the mineral grains are the remains of organisms living within the sediment. Biological constituents have unique environmental signatures that are more precise proxies for source areas than are mineral grains alone. They may be used to identify a single biofacies deposit (SBD) due to local sediment transport or a displaced, multiple biofacies deposit (MBD) resulting from staged sediment transport or a full-canyon flushing event. This Ascension-Monterey Canyon system study demonstrates that by using the biological constituents in marine deposits, the source areas and transport mechanisms may be identified. The 19,000 year record of core S3-15G captured hemipelagic mud interspersed with individual turbidites of sand and silt transported to the core site at lower bathyal depths (3491 m). The relative abundance of displaced benthic foraminifera was found to correlate positively with grain size, with 75% of the fauna being displaced in the cross-bedded turbiditic sand (Tc) units, 39% in the laminated turbiditic sand (Td) units, and 15% in the turbiditic mud (Tet) units. Nineteen samples were SBDs representing local canyon wall sloughing, bioerosion, or hemipelagic deposition at or near the core site. Sixty-five were MBDs, 31 of which were turbiditic sands originating in the estuarine to inner shelf, outer shelf, upper slope, or upper middle slope, and the remaining 34 were turbiditic muds with displacement initiated in the estuarine to inner shelf, outer shelf, and the upper slope. Commonly, the biological remains of several biofacies characterize these MBDs, reflecting staged sediment transport with storage occurring behind slumps that act as barriers to movement until finally released. Sediment bypassing, typically of the deeper biofacies, and full-canyon flushing, were also evident. Identifying and interpreting the distribution of allochthonous biological sediment constituents in marine deposits is a powerful tool in the investigation of sediment transport that can be applied to other submarine canyon systems. [ABSTRACT FROM AUTHOR]

Abstract: Subaqueous sediment density flows are one of the volumetrically most important processes for moving sediment across our planet, and form the largest sediment accumulations on Earth (submarine fans). They are also arguably the most sparely monitored major sediment transport processes on our planet. Significant advances have been made in documenting their timing and triggers, especially within submarine canyons and delta-fronts, and freshwater lakes and reservoirs, but the sediment concentration of flows that run out beyond the continental slope has never been measured directly. This limited amount of monitoring data contrasts sharply with other major types of sediment flow, such as river systems, and ensure that understanding submarine sediment density flows remains a major challenge for Earth science. The available monitoring data define a series of flow types whose character and deposits differ significantly. Large (>100km3) failures on the continental slope can generate fast-moving (up to 19m/s) flows that reach the deep ocean, and deposit thick layers of sand across submarine fans. Even small volume (0.008km3) canyon head failures can sometimes generate channelised flows that travel at >5m/s for several hundred kilometres. A single event off SE Taiwan shows that river floods can generate powerful flows that reach the deep ocean, in this case triggered by failure of recently deposited sediment in the canyon head. Direct monitoring evidence of powerful oceanic flows produced by plunging hyperpycnal flood water is lacking, although this process has produced shorter and weaker oceanic flows. Numerous flows can occur each year on river-fed delta fronts, where they can generate up-slope migrating crescentic bedforms. These flows tend to occur during the flood season, but are not necessarily associated with individual flood discharge peaks, suggesting that they are often triggered by delta-front slope failures. Powerful flows occur several times each year in canyons fed by sand from the shelf, associated with strong wave action. These flows can also generate up-slope migrating crescentic bedforms that most likely originate due to retrogressive breaching associated with a dense near-bed layer of sediment. Expanded dilute flows that are supercritical and fully turbulent are also triggered by wave action in canyons. Sediment density flows in lakes and reservoirs generated by plunging river flood water have been monitored in much greater detail. They are typically very dilute (<0.01vol.% sediment) and travel at <50cm/s, and are prone to generating interflows within the density stratified freshwater. A key objective for future work is to develop measurement techniques for seeing through overlying dilute clouds of sediment, to determine whether dense near-bed layers are present. There is also a need to combine monitoring of flows with detailed analyses of flow deposits, in order to understand how flows are recorded in the rock record. Finally, a source-to-sink approach is needed because the character of submarine flows can change significantly along their flow path. [Copyright &y& Elsevier]

Submarine canyons and associated submarine fans are in some cases located at the end of a littoral cell where they act as conduits for the transfer of eroded terrigenous sediments to the marine environment. Such fans are generally found in deep-water settings at >500 m water depth. Offshore the Moisie River Delta (NW Gulf of St. Lawrence, Eastern Canada), high-resolution multibeam bathymetry and seismic data led to the discovery of an unusually shallow submarine fan (≤60 m) located at the end of a littoral cell. Sediment is transported westward on the shallow coastal shelf, as demonstrated by the downcurrent displacement of oblique nearshore sandbars where the shelf narrows to less than 1 km. The steep slope near the end of the littoral cell is incised by a channel that feeds a submarine fan composed of smaller channels and depositional lobes. According to existing Holocene evolution models for the region, the fan formed within the last 5,000 years. Its evolution is largely due to the transport of sediment by longshore drift. Multibeam echosounder and seismic data also reveal that the gravity-driven accretion of the submarine fan is characterized mainly by two processes, i.e., frequent small-scale, downslope migration of sandwaves on the slope, and more episodic slumping/turbidity-current activity in the deeper part of the fan. This study documents that, besides their common deep-water location, smaller-scale submarine fans can occur also in very shallow water, implying that they could be more frequent than previously thought both in modern environments and in the rock record. [ABSTRACT FROM AUTHOR]

Submarine canyons are major conduits for sediment transfer from continental shelf to deep marine environments. Mass failures and faults play a key role in the initiation and evolution of submarine canyons along convergent tectonic margins, in addition to continental sediment supply. Here we analyze high-resolution bathymetry and seismic data from the Colombian southern Caribbean to investigate the controls on submarine canyon morphology along a convergent tectonic margin. We propose three end-member types of canyons: Type I canyons have a direct connection to a major river associated with high sediment supply. These canyons are highly erosive and cut topographic barriers created by tectonic deformation. Type II canyons are associated with faults at the canyon's head, where the location, orientation, and sinuosity are controlled by fault strike. Also, the presence of faults is related to an increase in the occurrence of mass failures from the steep canyon borders, increasing the depth and width asymmetry. Finally, Type III canyons evolve toward the continental shelf edge through retrogressive mass failures. These mass failures produce erosional scars that merge downslope to create submarine canyons in early stages of development, which later evolve to wider but shallow canyons due to the progressive basinward merging. We argue that the morphology of each canyon type is controlled by the interaction between continental sediment supply, mass failures, shelf width, and fault occurrence. We also demonstrate that seafloor topography influences the size of submarine fan deposits at the mouths of canyons. We identified large fan deposits (>650 km2) on the continental rise, whereas in piggyback sub-basins we found smaller fans (<60 km2). Our analysis of downdip canyon morphology and associated deposits can be used to predict the development of submarine canyons and associated fans in convergent tectonic margins worldwide. • Bathymetry and seismic data quantify submarine canyons on a convergent margin. • Three canyon types exist due to geomorphologic variability along the margin. • Sediment flux and shelf-slope topography affect canyon morphology and fill. • Submarine fan dimensions controlled by topographic confinement, or lack thereof. [ABSTRACT FROM AUTHOR]

Abstract: An approach combining interpretation of seismic reflection data with analysis of core lithology, especially analysis of the depositional ages of turbidites, showed that depositional patterns in the deep-sea basin of the eastern Kumano Trough, which is a forearc basin along an active convergent plate margin, were different during sea-level lowstand, slow transgressive, rapid transgressive, and highstand stages. During the lowstand and early transgressive stages, turbidites were deposited on the deep-sea basin floor where they formed a submarine fan composed of terrigenous sediments supplied by rivers via a submarine canyon. Subsequent coastline retreat and bay development during the rapid transgression stage caused a decrease in the amount of coarse-grained terrigenous sediments reaching the basin floor. However, turbidites were still deposited within the submarine canyon during the rapid transgressive and highstand stages. These deposits contain shelf sediments that have been reworked by tidal currents and storms, and sediments from slope failures caused by submarine earthquakes, but they do not contain the terrigenous sediments that are characteristic of the turbidites of the lowstand and slow transgression stages. [Copyright &y& Elsevier]

Abstract: The main feature of the Congo-Angola margin in the Gulf of Guinea is the Congo (ex-Zaire) deep-sea fan composed of a submarine canyon directly connected to the Congo River, a channel and a [sediment] lobe area. During the multi-disciplinary programme called BIOZAIRE conducted by Ifremer from 2000 to 2005, two CTD-O2 sections with discrete water column samples were performed (BIOZAIRE3 cruise: 2003–2004) to study the influence of the Congo River discharges, both in the surface layer and in the deep and near-bottom layers. The surface layer water is greatly diluted with river water that has a heavy particle load. The deep layer is affected by episodic turbidity currents that flow in the deep Congo channel and reach deep areas far from the coast. Previous studies revealed deep anomalies in oxygen (deficit) and nutrient (excess) concentrations at ∼4000m depth and assumed that they resulted from mineralisation of the particulate organic matter from the Congo River. The BIOZAIRE3 sections were designed to explore these phenomena in more detail near the Congo channel. Oxygen and nutrients were measured as well as additional parameters, including stable isotopes of oxygen and carbon, dissolved inorganic carbon and pH. For the surface layer, the effect of the Congo River was studied with reference to salinity. Deviations from the theoretical dilution of various inorganic solutes suggested the occurrence of mineralisation and consumption processes. For the deep layer, the network of CTD-O2 stations gave a more detailed description of the deep anomalies than in previous studies. From the east–west section, anomalies appeared on the bottom at 4000m depth and became slightly shallower when they spread to the west. They were also present north and south on the bottom along the 4000m isobath. In these deep waters, the decrease in the δ13C values of dissolved inorganic carbon confirmed that the mineralisation of organic matter plays a role in generating these anomalies. The location of the origin of this deep anomaly is debated. Here, arguments are given in favour of mineralisation of the particulate organic matter input that overflows from the Congo channel at ∼4000m depth during turbidity current events. Other authors suggest that this input comes from downslope particle transport. Anomalies of the same origin, but weaker, also occurred deeper on the Congo lobe, where the Congo channel ends, but with a significant pH decrease on the bottom which was not seen at 4000m depth. [Copyright &y& Elsevier]

Abstract: The Congo deep-sea fan is one of the largest fans in the world still affected by presently active turbidity currents. The present activity of deep-sea sedimentary processes is linked to the existence of a direct connection between the Congo River estuary and the Congo canyon head that allows relatively continuous sediment feeding of the deep-sea environment, in spite of a wide continental shelf (150km). Because of this important activity in terms of sedimentary processes, the deep-sea environment of the Congo–Angola margin presents major interests concerning physical, chemical and biological studies near the seafloor. The main aim of this paper is to present the initial geological context of the BioZaire Program, showing a synthesis of the major results of the ZaïAngo Project including (1) the brief geological setting of the Congo–Angola margin, (2) the structure of the modern Congo deep-sea fan, (3) the sedimentary architecture of the recent Congo turbidite system (from the canyon to the distal lobes) and (4) the recent and present turbidite sedimentation. In order to provide useful information and advice relevant to biological and geochemical studies across the Congo sedimentary system, this article is particularly focused on the present sedimentary processes and the present activity of turbidity current along the Congo canyon and channel. [Copyright &y& Elsevier]

Multibeam sonar data, acoustic sub-bottom profiles and box cores were used to study the activity of submarine canyons and fans near the city of Les Escoumins, on the North Shore of the Lower St. Lawrence Estuary (Eastern Canada). The multibeam data were used to generate a high-resolution digital terrain model that reveals the presence of a large number of canyons and fans along the northern slopes of the Laurentian Channel. This paper focuses on two of the larger canyons, and their associated submarine fans. The sub-bottom profiles on the fans reveal high-amplitude reflections at the sediment/water interface and near the seafloor surface, indicating the occurrence of layers of coarse material. A turbidite was observed in a box core sampled in one of the fans, confirming the nature of the coarse layer. Geophysical and sedimentological data indicate that the canyons and fans play an important role in transferring coastal sandy sediments to the deeper marine environments by longshore drift-initiated turbidity flows, and thereby contribute to the negative sediment budget along the coast. The morphology of the canyons indicates that they were produced by a combination of erosive turbidity flows and retrogressive failures. The two box cores sampled on the fans reveal a recent (~last 60 years) quasi-exponential increase in sand content near the surface of the cores, possibly reflecting recent deforestation and/or increased coastal erosion. [ABSTRACT FROM AUTHOR]

Abstract: We have integrated the relatively unknown distal domains of the Lower Congo basin, where the main depocenters of the Congo submarine fan are located, with the better-constrained successions on the shelf and upper slope, through the analysis of thousands of km of 2D seismic reflection profiles off-shore the Congo–Angola passive margin. The basin architecture is depicted by two ca. 800-km-long regional cross sections through the northern (Congo) and southern (Angola) margin. A large unit deposited basinward of the Aptian salt limit is likely to be the abyssal-plain equivalent of the upper-Cretaceous carbonate shelf that characterized the first post-rift deposits in West-equatorial African margins. A latest-Turonian shelf-deepening event is recorded in the abyssal plain as a long period (Coniacian–Eocene) of condensed sedimentation and basin starvation. The onset of the giant Tertiary Congo deep-sea fan in early Oligocene following this event reactivates the abyssal plain as the main depocenter of the basin. The time–space partitioning of sedimentation within the deep-sea fan results from the interplay among increasing sediment supply, margin uplift, rise of the Angola salt ridge, and canyon incision throughout the Neogene. Oligocene–early Miocene turbidite sedimentation occurs mainly in NW–SE grabens and ponded inter-diapir basins on the southern margin (Angola). Seaward tilting of the margin and downslope salt withdrawal activates the up-building of the Angola escarpment, which leads to a northward (Congo) shift of the transfer zones during late Miocene. Around the Miocene–Pliocene boundary, the incision of the Congo submarine canyon confines the turbidite flows and drives a general basinward progradation of the submarine fan into the abyssal plain The slope deposition is dominated by fine-grained hemipelagic deposits ever since. Results from this work contribute to better understand the signature in the ultra-deep deposits of processes acting on the continental margin as well as the basin-wide sediment redistribution in areas of high river input. [Copyright &y& Elsevier]

Abstract: Sand-rich submarine fans are radial or curved in plan view depending on the slope of the basin floor. They occur isolated or in coalescing systems. The fans'' average lateral extent measures close to 25 km and their thickness usually less than 300 m. The thickness of outer fan sequences averages around 120 m and that of middle fan successions around 160 m. Rarely reported inner fan sequences have a maximum thickness of 80 m. The formation of sand-rich fans is closely related to tectonic activity. Their sediment is coarse-grained and compositionally immature as indicated by significant feldspar content due to close provenance and rapid transport by short rivers with a steep gradient controlled by tectonism. Tectonic activity also provides for narrow shelves making the fans relatively insensitive to sealevel changes. Formation of sand-rich fans typically occurs in restricted continental basins. The tectonic settings are highly variable. Sand-rich fans typically receive their sediment through submarine canyons which intercept sand from longshore drift and/or are fed more or less directly by regional rivers. The type of ancient fan system (radial, curved, isolated, coalescing) may be identified through paleocurrent map plots, facies map sketches, recognition of lateral thickness variations and sediment influx centers, as well as lateral bed correlations defining the minimum fan extent. Important in distinguishing different environments of ancient fans are detailed measured sections, their comparison and correlation. Channelized inner fan and middle fan deposits may be distinguished from the unchannelized outer fan successions through bed correlation tests which reflect their different stratigraphic architectures and bedding patterns. Bedding in outer fan deposits (lobes) is relatively simple, parallel, and regular. The lateral bed continuity is relatively high. Channel fills, especially those of middle fan distributary channels, display a complicated bedding pattern with vertical and lateral random distribution of channel fills, axial erosion, and bed convergence towards the channel margins. Channel fills exhibit only linear bed continuity. Thus, the probability in carrying out local to regional scale lateral bed correlations is almost exclusively limited to outer fan deposits. The measured sections will help further distinguish fan environments by revealing: (1) different facies associations in outer fan sequences (mainly B, C and D) and middle fan successions (mainly A, B, C, D, and channel margin facies); (2) greater average bed and layer thicknesses in middle fan as opposed to outer fan successions (“bed” and “layer” as used herein); (3) more frequent amalgamation surfaces in channel fills than in unchannelized outer fan deposits; (4) more frequent tabular amalgamation surfaces in outer fan sections; (5) more frequent nontabular amalgamation surfaces in channel fills; and (6) more frequent dish structures in middle fan than outer fan successions. Rarely exposed fan valley fills may be identified by coarse conglomerates. Moreover, in proximity to fan valley fills, relatively mud-rich sediments may be observed that derive from the depositional system of the basin slope. [Copyright &y& Elsevier]

It is well established that sedimentary margins grow by sediments bypassing through shelf- and slope-incising canyons onto the basin floor and by sediments being deposited incrementally across clinoforming and prograding margins. However, we argue that these two distinctive types of deep-water sediment supply to the basin floor and to the margin are generally not operating at the same time and should not be seen as integral parts of a single model. When shelf-incising canyons were actively bypassing sediments across the margin, the margin itself was not prograding, and vice versa. We present stratigraphic data for some 111 global examples of shelf- and slope-incising canyons and their linked basin-floor sediments, and we provide criteria to distinguish them from prograding margins fed by shelf-edge deltas and their linked slope channels and toe-of-slope fans. The defining character of the canyon feeding system is basin-floor sediment aggradation and the onlapping of this stratigraphy against an eroded basin margin. For many of our examples this onlap persists for millions to tens of millions of years and is especially prolonged in periods of persistent high eustatic sea level. This is in clear contrast to the downlapping stratigraphy that dominates during intervals of high sediment supply from the shelf, and active margin accretion. Some 60% of the ancient canyon/basin-floor fan systems are inferred to have been sourced by canyons tapping longshore drift in littoral cells; they are inferred because with canyon capture, tapped littoral cells are generally depleted and not preserved. In other cases, shelf-incising canyons tapped documented deltas on the inner or middle shelf, but in some other cases, a deltaic or riverine source was inferred. Canyon cutting and initial sediment bypass through the canyons are chiefly associated with initially 'out-of-grade' margins—for example, where a carbonate margin has foundered and oversteepened or where large-scale collapse of aggradational and oversteepened clastic shelf edges occurred. Canyon feeding onto the basin floor is linked with runout of basin-floor fans to the basin center, in contrast to direct-fed prograding margins, where sediment is continuously partitioned onto and across the entire shelf-edge, slope, and toe-of-slope areas. [ABSTRACT FROM AUTHOR]

Submarine canyons play a major role in sediment transfer to the deep sea. When connected with fluvial systems, they can produce large submarine fans, whose sandy bodies have a high potential as petroleum reservoirs. Although canyon-river connections are common on passive margins during lowstands, they are rare during highstands. So far, the only canyon in the Western South Atlantic to have exhibited continuous river connection throughout the Quaternary, regardless of sea level position, is the São Francisco Canyon (SFC) in eastern Brazil. In this study, we used multibeam and 3D seismic records integrated with previously published data to investigate the reasons for the continuous canyon-river connection in the area of the São Francisco River. The SFC comprises two compartments: The Upper and the Mid Canyon. The Upper Canyon indents 15 km of the shelf and acts as an erosive feeder trunk to the São Francisco Submarine Fan. When it emerges on the continental slope (Mid Canyon), depositional processes dominate; the canyon now begins to meander and the thalweg is bordered by numerous terraces and levees. Five stratigraphic units have accumulated in the region of the canyon head since the beginning of the Oligocene. Initially, sedimentation had a uniform aggradational character (Unit 1), which later became more discontinuous in association with the development of reef build-ups (Unit 2) and of a low-lying area around the canyon head. This depression was partially infilled by siliciclastics (Unit 3) and later incised by a precursor of the SFC (Unit 4). The depression still has a morphological expression in the shelf nowadays as a bathymetric low (BL), within which the São Francisco River has built its delta (Unit 5). We hypothesize that the origin and evolution of the SFC is associated with three main factors: (i) breaching by the canyon head of thick carbonates rimming the shelf break; (ii) development of the shelf depression referred above; and (iii) major continental drainage reorganization. Continuous canyon-river connection was ensured by this shelf depression, which helped funnel siliciclastic sediments to the canyon and precluded lateral changes to the lower river trunk. Morphological features, such as axial incision of mass movement deposits is suggestive of some, although very limited, modern canyon activity. This case study contributes to a better understanding of river-basin sediment pathways, particularly on passive margins, which are of great importance for the successful exploration of submarine fan systems. • Shelf morphology controlled canyon-river connection in a narrow passive margin • Distribution of shelf-break reef buildups controlled degree of canyon shelf indentation • A shelf bathymetric depression ensured continuous delta-canyon connection • Morphological features indicate modern, although limited, canyon activity [ABSTRACT FROM AUTHOR]

Continental margins usually display along-strike morphological variation, with diverse underlying controls around the world. Based on 3D seismic data from the Baiyun Sag, northern South China Sea, this work provides a new case study to understand the combined controls on along-strike morphological variation over short strike distances. The northern slope of the Baiyun sag was characterized by a gently dipping ramp at the beginning of the Quaternary, and the Quaternary along-strike morphological variation in this area is mainly displayed in the deltas, submarine canyons and contourite depositional system. The deltas were featured by lobate form and mainly distributed at the western area, with shoreline parallel and oblique to the ramp strike in the west and east, respectively. The scales of the deltas and the associated submarine canyons decreased towards the east. The eastern plastered contourite drifts have a greater areal extent than those in the west, and the former are terraced. The Quaternary slope evolution took place in three stages (stage 1–3), of which the time intervals are ca. 2.6 - ca. 1.6 Ma, ca. 1.6 - ca. 0.14 Ma and ca. 0.14–0 Ma, respectively. The slope was characterized by a gentle ramp, deltas and contourites from stage 1–3 respectively. The along-strike morphological variation of the northern slope of the Baiyun Sag was predominantly influenced by the interplays between the deltas, pre-existing morphology, and oceanographic regimes. The localization of the lobate-form deltas with respect to the pre-existing submarine canyons on the ramp exerted a great influence on the along-strike variation of these canyons within stage 2. The interplay between the delta morphology (i.e., delta position and delta-front gradients) and the oceanographic regimes (i.e. contour currents and internal waves) controlled the along-strike variation in contourite processes during the stage 3. This study provides a new insight into the combination of controls responsible for along-strike morphological variation of post-rift continental margins evolving from a ramp. The underlying depositional processes revealed by this study would be helpful for understanding the lateral variability of sequence architectures and the deep-water sands deposition, which are important basis for guiding future deep-water hydrocarbon exploration on such continental margins elsewhere. ● The northern slope of the Baiyun Sag displays along-strike morphological variability ● Lobate-form delta localization influences the along-strike variation of canyons ● Interplay between delta morphology and oceanographic regimes influences contourite processes [ABSTRACT FROM AUTHOR]

The present work simulated a hypothetical 4D delta-canyon-fan depositional system using stratigraphic forward modelling (SFM) to: 1) investigate the differences and linkages of the sea-level control on the evolution of each sub-environment; 2) explain the evolution under the constraints of sea-level change from the perspective of channel activities. The SFM approach LECODE applied in this study combines an open-channel flow approach with a non-uniform sediment transport algorithm, with former to simulate water dynamics of turbidity currents and river flows and latter to simulate the transportation, deposition, and erosion of sediments. The input data is calibrated via sensitivity analysis and survey of analogue records. The results are compared with three sets of actual seismic data as verification. After introducing the general characteristics of the model, this study compares the influence of sea-level change on the delta, canyon, and fan, respectively, by analysing stratigraphic framework, the architecture of channel-levee complex, channel distribution and migration, sedimentation/erosion rate, and peak velocity. Moreover, a higher sediment supply case and a lower sediment supply case are compared to test the situation when sediment supply is less dominant. Finally, the influence of sea-level change on channel migration is discussed and the system evolution, especially the canyon evolution, is explained from the view of channel activities. The results show that sea-level control will be weakened from the delta to the fan via the canyon along with sediment transport. With higher sediment supply, the weakening is stronger. With lower sediment supply, the whole system is more sensitive to the sea-level change and this sensitivity lasts longer. The channel migration is more influenced by local topography, even adjacent topography, rather than sea-level change. The inner bank erosion near the canyon head is directly related to the shelf morphology. The translation and asymmetrical distribution of turbidity channels result in the translation and asymmetrical erosion of canyon bends. The insights extracted from this study could discriminate sea-level control on submarine canyon and fan instead of regarding them as an entirety of ultimate sink in source-to-sink research. Also, the integrated investigation with both qualified perspectives and quantified data could refine sequence stratigraphic concepts and provide a prototype for hydrocarbon exploration on high-sediment-supply river-fed delta-canyon-fan systems. • A delta-canyon-fan model using process-based stratigraphic forward approach. • Control of sea-level change weakens from canyon to fan. • High sediment supply strengthens the weakening effect of sea-level change control. • Local bathymetry dominate channel migration rather than sea-level change. • Evolution curves of deposition and current velocity against sea-level change. [ABSTRACT FROM AUTHOR]

The continental slope and rise seaward of the Totten Glacier and the Sabrina Coast, East Antarctica features continental margin depositional systems with high sediment input and consistent along-slope current activity. Understanding their genesis is a necessary step in interpreting the paleoenvironmental records they contain. Geomorphic mapping using a systematic multibeam survey shows variations in the roles of downslope and along slope sediment transport influenced by broad-scale topography and oceanography. The study area contains two areas with distinct geomorphology. Canyons in the eastern part of the area have concave thalwegs, are linked to the shelf edge and upper slope and show signs of erosion and deposition along their beds suggesting cycles of activity controlled by climate cycles. Ridges between these canyons are asymmetric with crests close to the west bank of adjacent canyons and are mostly formed by westward advection of fine sediment lofted from turbidity currents and deposition of hemipelagic sediment. They can be thought of as giant levee deposits. The ridges in the western part of the area have more gently sloping eastern flanks and rise to shallower depths than those in the east. The major canyon in the western part of the area is unusual in having a convex thalweg; it is likely fed predominantly by mass movement from the flanks of the adjacent ridges with less sediment input from the shelf edge. The western ridges formed by accretion of suspended sediment moving along the margin as a broad plume in response to local oceanography supplemented with detritus originating from the Totten Glacier. This contrasts with interpretations of similar ridges described from other parts of Antarctica which emphasise sediment input from canyons immediately up-current. The overall geomorphology of the Sabrina Coast slope is part of a continuum of mixed contourite-turbidite systems identified on glaciated margins. • The slope and rise off the Totten Glacier feature sediment ridges between submarine canyons. • Sediment ridges in the east are formed from turbidity currents flowing in adjacent canyons and a pelagic component. • In the west, larger ridges are formed from widespread hemipelagic and contouritic sedimentation. • The western ridges are separated by a submarine canyon with a convex thalweg mostly sourced from the ridge flanks. [ABSTRACT FROM AUTHOR]

Based upon new seismic reflection data, this study reveals the development of a complex sedimentary system on the lower-slope terrace off Maputo on the southern Mozambique margin. The deep-water sedimentary system clearly shows the interaction of downslope and alongslope processes. Downslope features include: a pronounced canyon, slope creep, submarine slides, and multi-stage mass-transport deposits. Alongslope features include: contourite drifts and sediment waves, erosional moats, valleys, erosive surfaces and a distinctive contourite terrace. We show an evolution through time as follows: (1) restricted marine sedimentation during the Early Cretaceous after the initial break-up, with slope progradational clinoforms and hemipelagite drape developed; (2) open marine sedimentation characterized by the onset of alongslope sedimentary processes during the Late Cretaceous and development of a contourite depositional system; (3) downslope gravity processes dominated sedimentation during the Paleocene-Eocene, including development of a canyon and submarine fan; and (4) an alongslope contourite depositional system was re-established on the lower slope in the Middle Miocene, while turbidites (from a northern source) covered the Mozambique Basin. The Mozambique Fracture Zone marks a distinct and steep slope seaward of the contourite terrace, and has significantly influenced both contourite and turbidite deposition. Our study provides new insights into the onset and evolution of bottom current control on margin sedimentation, the interaction of downslope and alongslope processes and how these processes have jointly sculpted this part of the southern Mozambique margin. • Depositional features of a complex deep-water sedimentary system are investigated. • Late Cretaceous onset of current-controlled deposition. • Downslope-alongslope interaction in constructing the continental margin. • The Mozambique Fracture Zone significantly influenced contourite and turbidite deposition. [ABSTRACT FROM AUTHOR]